The major objective of this project is to characterize host immune responses in filariasis and relate the findings to pathogenesis and/or protection. Quantitative and qualitative aspects of IgE responses are being rigorously characterized. Highly sensitive radioimmunoassays and crossed radioimmunoelectrophoresis have been developed to identify filarial allergens to which the IgE antibodies' response is directed. In addition, IgG responses are also being quantitated and their importance in blocking IgE-mediated responses is under investigation. Characterization of antigens from different stages of the parasite (infected larvae, L3, and microfilaria) as well as excretions and secretions and surfaces is being carried out using immunochemical techniques to identify unique and common antigens. Such information should prove useful in developing immunodiagnostic reagents and also identify antigens important in disease protection.